Seeing the Light - Bringing Plasmonic Nanofields Into Focus

Image of a bowtie structure from a web-based imaging toolkit designed for researchers studying plasmonic and photonic structures. This open-source software, called Plasmonics Toolkit, is available at http://www.nanohub.org.

Scanning electron images of a nanoscale bowtie antenna. With the vertical bowtie antenna shifted 5 nanometers left of center, the two plasmonic modes are spectrally and spatially distinct while maintaining nanoscale mode volumes (a, b). Using a novel imaging concept, the two modes were experimentally visualized and their respective positions measured to be at the X marks in (c). These mode positions are known with nanoscale accuracy – 100 times better than the diffraction limit!

A research team led by the Molecular Foundry's Jim Schuck demonstrated an innovative imaging concept to visualize plasmonic fields from devices with nanoscale resolution. In plasmonic devices, electromagnetic waves crowd into tiny metal structures, concentrating energy into nanoscale dimensions. This savvy coupling of electronics and photonics could be harnessed for high-speed data transmission or ultrafast detector arrays.

However, studying plasmonic fields in nanoscale devices presents a real roadblock for scientists, as examining these structures inherently alters their behavior. Previously, the team engineered bowtie-shaped plasmonic devices to steer light at the nanoscale. These nano-color sorter devices focus and sort light in tiny spaces to a desired set of colors or energies—crucial for detectors.

Now, by imaging fluorescence from gold within an bowtie and maximizing the number of photons collected, the team gleaned the position of plasmonic modes—oscillations of charge that result in optical resonance—just a few nanometers apart.

In parallel, the team developed a web-based toolkit designed to calculate images of plasmonic devices to simulate how changing the size and symmetry of a plasmonic antenna affects its optical properties. This toolkit is freely available for other researchers to download on http://www.nanohub.org, a computational resource for nanoscience and technology.